Vicky wanted to investigate water evaporation. She placed 50 mL of distilled water in three identical glass jars. She left one jar in the sunlight, one jar in the dark, and one jar in a shady area. After four hours, she measured how much water was still in each jar. Which of the following variables was held constant in the experiment? A. air temperature B. amount of water in jars at the end of the investigation C. light exposure D. amount of water placed in jars